The use of weight filling systems with highly heterogeneous products or products which have solid or semi-solid suspended elements with variable dimensions and compactness is rather problematic.
The known weight filling methods are all characterized by filling valves connected to a tank or a collector, and the dynamics of opening/closing the valve depend on the strategy for measuring the weight of the product dispensed. The spillage of the product from the valves is promoted by the pressure caused by the geodetic head of the product itself or by a slight pressurization (a few meters of water column at maximum) of the tank or collector which supplies the product to the valves.
In addition to requiring constant mixing to avoid the stratification of the solid parts due to the difference in density, the heterogeneous products have the problem that certain pieces tend to aggregate close to the outlet of the valves, thus compromising the correct filling strategy.
In order to ensure continuity to such an operation, a pressurization scheme needs to be applied to the product, which is incompatible with weight measurement systems but is typical of volumetric filling systems. This type of method is based on volumetric piston systems. These systems are physically incapable of ensuring actual filling constancy because as the physical variables of the product change, such as for example the temperature or the distribution of the suspended pieces at different densities, the dispensing at constant volume changes the weight quantity filled in the container and the resulting quantity of product actually packaged.
Considering that legislation considers the weight of the packaged product as the reference declaration on the label, volumetric systems require over-filling the container in order to avoid sanctions should underweight products be introduced in the market. Thereby, more product is given to the user than what is purchased, with resulting increases in production costs.